During the past few years, extensive efforts have been made to provide flame-retarded carpets for both residential and commercial buildings. One of the best flame retardants for this purpose was found to be alumina hydrate (Al.sub.2 O.sub.3. 3H.sub.2 O), also referred to as "hydrated alumina". This material not only provides excellent flame-retarding properties, but is also nontoxic and readily utilizable in the carpet industry. The alumina hydrates employed as flame-retarding agents for carpets generally result from the extensive refining of bauxite and are characterized by high purity and substantially uniform physical and chemical characteristics. Since alumina hydrate, as mentioned before, results from the purification of bauxite and its manufacture involves a large number of processing steps, it is not an inexpensive material and sometimes, due to its wide application in other areas, is not always readily available. Consequently, there has been a continuing need for a flame-retarding agent which is available in nearly unlimited quantity, does not exhibit toxic properties and, last but not least, does not have to undergo extensive refining before use in the carpet industry.
Logically, bauxite, the native ore of alumina hydrate, would be such a suitable flame-retarding agent. However, bauxites do not possess uniform chemical and physical characteristics, their appearance and compositon vary from geographical location to geographical location and even within the same geographical location, bauxites can differ in properties from local mining site to mining site. This large variation in properties seemed to pose insurmountable problems and discouraged those skilled in the art from using bauxite as a flame-retarding agent for the carpet industry. This was further emphasized by the fact that even the high purity alumina hydrate did not always perform satisfactorily in the polymer compositions utilized in the carpet industry. Thus, to alleviate some of the problems associated with the use of alumina hydrate in latex foams, U.S. Pat. No. 3,699,041--Sanderford et al recommends the use of surface modifiers to render the alumina hydrate compatible with latex compositions. In U.S. Pat. No. 3,874,889--Geppert et al, it is disclosed that alumina hydrate-filled latex foam collapse can be prevented by treating ground alumina hydrate with water at a selected temperature prior to use in the latex compositions.
It has now been discovered that regardless of the impure nature of bauxite and its nonuniform properties, bauxite can be successfully employed as a flame-retarding filler for polymer compositions such as utilized in the carpet industry. The bauxites, which can readily replace alumina hydrate as a flame-retarding filler in polymer compositions, are characterized by a surface area of less than about 12 m.sup.2 /g when dried at about 100.degree. C. for about one hour; a particle size distribution after grinding wherein not more than about 15% by weight of the particles have a size of less than about 3 microns and a pH in aqueous suspension which is in excess of about 6.5.
It has been found that these characteristics are interrelated and if any of these parameters are outside the limits shown, the bauxite will not perform satisfactorily in the polymer compositions. Unsatisfactory performance manifests itself in the accelerated thermal aging properties of polymer foams and/or unsuitably high viscosities in polymer precoat and adhesive compositions filled with bauxites which do not meet the above criteria. It has been further discovered that bauxites which possess a surface area between about 12 and about 20 m.sup.2 /g can also be rendered suitable for incorporation as flame-retardant in polymer compositions utilized in the carpet industry when their surfaces are modified with an inorganic phosphate or silicate, or with an aliphatic or aromatic hydrocarboxylic acid, such as tannic acid or citric acid or salts of citric acid.